A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface.
It is desirable at times to erase all data stored on a HDD. One approach for erasing all data stored on a HDD is to use a bulk eraser apparatus. FIG. 1 is a diagram of bulk eraser apparatus 2 according to known techniques. As shown in FIG. 1, bulk eraser apparatus 2 comprises magnets 6 and 8 which generate magnetic circuits 10 and 12 respectively. Magnetic circuit 10 flows in a clockwise (or counterclockwise) direction, while magnetic circuit 12 flows in a counterclockwise (or clockwise) direction. During HDD bulk erase operation, HDD 4 is moved to position 14 while the magnetic recording disks of HDD 4 are spinning at normal operating speed or any other specific rotating speed. Magnetic circuit 10 and 12 are designed such that they flow primarily parallel to the magnetic recording disks within HDD 4. The direction of the magnetic field running through HDD 4 is depicted in FIG. 1. Importantly, by positioning HDD 4 in position 14, the direction of the magnetic field is designed to run through the magnetic information on the magnetic recording disk, but allow the motor within HDD 4 to be largely unaffected by the magnetic field. The magnetic field flowing in a parallel direction through the magnetic recording disks of HDD 4 cause the polarity of the magnetic information stored on the magnetic recording disks within HDD 4 to hold random values after HDD 4 is withdrawn from bulk eraser apparatus 2, thereby erasing data stored on the magnetic recording disks of HDD 4.